U.S. patent number 5,803,099 [Application Number 08/557,633] was granted by the patent office on 1998-09-08 for ultrasonic cleaning machine.
This patent grant is currently assigned to Furuno Electric Co., Ltd., Matsumura Oil Research Corp.. Invention is credited to Genzi Mori, Yukio Morimoto, Shinichi Sakuta, Toyoki Sasakura.
United States Patent |
5,803,099 |
Sakuta , et al. |
September 8, 1998 |
Ultrasonic cleaning machine
Abstract
The present invention provides flexibility in the shape and
material of the cleaning vessel, enables high-power transmission of
ultrasonic waves, and reduces audible noise generation. An
ultrasonic cleaning machine according to the invention comprises an
acoustic lens mounted above an ultrasonic transducer which is
immersed in oil held within an external tank as well as a cleaning
vessel holding a cleaning liquid further above the acoustic lens so
that ultrasonic waves produced by the ultrasonic transducer
converge at a point within the cleaning liquid. In one form of the
invention, the cleaning vessel is eliminated and the cleaning
liquid is held directly in the external tank.
Inventors: |
Sakuta; Shinichi (Kobe,
JP), Mori; Genzi (Kobe, JP), Sasakura;
Toyoki (Ashiya, JP), Morimoto; Yukio (Kobe,
JP) |
Assignee: |
Matsumura Oil Research Corp.
(Nishinomiya, JP)
Furuno Electric Co., Ltd. (Nishinomiya, JP)
|
Family
ID: |
17611638 |
Appl.
No.: |
08/557,633 |
Filed: |
November 14, 1995 |
Foreign Application Priority Data
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Nov 14, 1994 [JP] |
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6-279480 |
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Current U.S.
Class: |
134/56R; 134/58R;
68/3SS; 310/335; 134/184; 134/105 |
Current CPC
Class: |
B08B
3/12 (20130101) |
Current International
Class: |
B08B
3/12 (20060101); B08B 003/10 () |
Field of
Search: |
;134/56R,57R,58 R-184/
;134/105 ;310/315,341,346,335 ;236/1F ;68/355 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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1036602 |
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Aug 1958 |
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DE |
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62-281431 |
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Dec 1987 |
|
JP |
|
636049 |
|
Dec 1978 |
|
SU |
|
Primary Examiner: Stinson; Frankie L.
Attorney, Agent or Firm: Jordan and Hamburg
Claims
What is claimed is:
1. An ultrasonic cleaning machine comprising:
an external tank holding an insulating oil;
an ultrasonic transmitting device immersed in the insulating
oil;
a cleaning vessel holding a cleaning liquid, said cleaning vessel
being partially submerged in the insulating oil;
an ultrasonic wave focusing means, totally immersed in said
insulating oil and suspended above said ultrasonic transmitting
device and under said cleaning vessel, for focusing ultrasonic
waves produced by said ultrasonic transmitting so as to converge
within the cleaning liquid in the cleaning vessel.
2. An ultrasonic cleaning machine according to claim 1 further
comprising:
a power controller for controlling output power radiated by said
ultrasonic transmitting device by outputting a control output to
said ultrasonic transmitting device;
a temperature sensor for sensing temperature of the insulating oil;
and
said power controller being responsive to an output from said
temperature sensor so as to compensate said control output in
accordance with a temperature of said insulating oil to provide a
constant cleaning effect in said cleaning liquid regardless of oil
temperature variations.
3. An ultrasonic cleaning machine comprising:
an external tank holding an insulating oil;
an ultrasonic transducer immersed in the insulating oil;
an acoustic lens fixed above and apart from a radiating surface of
said ultrasonic transducer, wherein said radiating surface of said
acoustic lens is immersed in said insulating oil; and
a cleaning vessel holding a cleaning liquid, said cleaning vessel
being partially submerged in the insulating oil and above said
acoustic lens such that focusing characteristics of said acoustic
lens determined by said acoustic lens and acoustic characteristics
of said insulating oil direct ultrasonic waves produced by said
ultrasonic transducer through a bottom of said cleaning vessel to
converge within the cleaning liquid.
4. An ultrasonic cleaning machine comprising:
an external tank holding an insulating oil;
a cleaning vessel holding a cleaning liquid, said cleaning vessel
being partially submerged in the insulating oil; an ultrasonic
transmitting and converging device immersed in the insulating oil
and focusing ultrasonic waves to converge within the cleaning
liquid;
a pair of signal generators for generating signals of two different
frequencies which are used to control output power radiated by said
ultrasonic transmitting and converging device;
a temperature sensor for sensing a temperature of the insulating
oils; and
means for controlling the signals of the two different frequencies
for driving said ultrasonic transmitting and converging device such
that said two different frequencies are alternately chosen based on
a duty ratio set in accordance with said oil temperature to provide
a constant cleaning effect regardless of oil temperature
variations.
Description
FIELD OF THE INVENTION
This invention relates to an ultrasonic cleaning machine.
DESCRIPTION OF THE PRIOR ART
FIG. 1 is a general configuration diagram showing a typical example
of conventional ultrasonic cleaning machines. An oscillating
circuit 3 generates a 28 kHz signal, for instance. This signal is
amplified by a power amplifier 4 to cause an increase and converted
into ultrasonic vibration by ultrasonic transducers 5 that are
attached to the bottom of a cleaning vessel 53 from underside. (It
is to be noted that although there is shown only a single array of
transducers 5 in FIG. 1, they are actually attached to the whole
bottom surface of the cleaning vessel 53.) The ultrasonic vibration
produced by the ultrasonic transducers 5 penetrates the cleaning
vessel 53 and propagates to a cleaning liquid X held in the
cleaning vessel 53. If an object to be cleaned is immersed in the
cleaning liquid X, ultrasonic waves hit its surface and resultant
cavitation and/or ultrasonic streaming removes dirt from the
surface of the object.
Although ferrite was conventionally used in producing vibrating
elements 5-1 of the ultrasonic transducers 5, the use of ceramics
is most popular today. Generally, the individual vibrating elements
5-1 are bolted to appropriate support members and bonded to the
bottom of the cleaning vessel 53 with epoxy adhesive Q. The
cleaning vessel 53 is usually made of stainless steel to prevent
corrosion.
The aforementioned conventional ultrasonic cleaning machines have
some common problems, which are given below:
(1) The cleaning vessel 53 is limited in its shape and materials.
Since the ultrasonic transducers 5 are directly adhered to the
bottom of the cleaning vessel 53, the cleaning vessel 53 must have
a flat bottom and its material is limited to metal. For this
reason, it is practically impossible to use a tank of a complex
shape made of molded resin, for example.
(2) Transmitted ultrasonic energy is limited in its level. To
obtain high cleaning effect, it is necessary to increase the level
of ultrasonic energy incident upon a unit surface area of an object
to be cleaned. It is, however, impossible to drive the ultrasonic
transducers 5 with such high power that exceeds their tolerable
level because excessive input power can cause heat generation or a
breakdown of the ultrasonic transducers 5.
(3) Bonded surfaces of the ultrasonic transducers 5 can deteriorate
due to heat generation and vibration. When affected by heat and
vibration, the layer of adhesive Q which holds the ultrasonic
transducers 5 to the bottom of the cleaning vessel 53 may break,
allowing the transducers 5 to come off.
(4) Dirt adhering to fingers and fingernail s is difficult to
remove. When hit by ultrasonic waves, human nerves and bones suffer
a severe pain or an unpleasant feeling. If a hand is exposed to
ultrasonic waves in the cleaning vessel 53, one would scarcely have
any unpleasant feeling in his or her fingertips or fingernails, but
a severe pain would occur in the palm and back of the hand. This is
because the ultrasonic vibration propagates in the form of
progressive waves from the ultrasonic transducers 5 mounted on the
bottom of the cleaning vessel 53 and hits the whole surface of the
hand soaked in the cleaning liquid X held in the cleaning vessel
53. It is therefore essential to control the input power fed into
the ultrasonic transducers 5 to such a level that will not cause
pains to human hands. This is likely to result in an inability to
provide sufficient cleaning effect.
(5) Unpleasant noise is generated when an ultrasonic cleaning
machine is operated. Although ultrasonic waves for exciting the
ultrasonic transducers 5 have,frequencies higher than the audible
range, it is known that the ultrasonic cleaning machine generates a
high-pitched sound which is quite unpleasant to the human ear. This
noise results from secondary vibration of the cleaning vessel 53
within the audible frequency range. The noise occurs because
vibrating surfaces of the ultrasonic transducers 5 are directly
bonded to the metallic surface of the cleaning vessel 53.
SUMMARY OF THE INVENTION
Having summarized an example of the conventional ultrasonic
cleaning machine, it is an object of the present invention to solve
the above-described problems of the prior art.
According to one aspect of the invention, an ultrasonic cleaning
machine comprises an external tank holding an insulating oil, an
ultrasonic transmitting and converging device immersed in the
insulating oil, and a cleaning vessel holding a cleaning liquid,
the cleaning vessel being partially submerged in the insulating
oil, wherein ultrasonic waves produced by the ultrasonic
transmitting and converging device converge at a single point
within the cleaning liquid.
In thus constructed ultrasonic cleaning machine, the cleaning
vessel is so located that the ultrasonic waves converge within the
cleaning liquid. When an object to be cleaned is positioned at the
converging point, ultrasonic energy incident upon a unit surface
area of the object is increased and a maximum cleaning effect is
obtained. If viscosity of the insulating oil is affected by its
temperature variations to a large extent, the ultrasonic cleaning
machine may additionally be provided with a power controller and a
temperature sensor for controlling output power in order to
maintain a constant cleaning effect.
In one form of the invention, the ultrasonic transmitting and
converging device of the above ultrasonic cleaning machine includes
an ultrasonic transducer and an acoustic lens. The acoustic lens
may be mounted either at a certain height above or in close contact
with a radiating surface of the ultrasonic transducer. In the
former case, it is possible to move up and down the converging
point of the ultrasonic waves although there is the need for a
support mechanism for retaining the acoustic lens in the insulating
oil. In the latter case, mechanical construction can be simplified
because such a lens support mechanism is not required although the
converging point can not be moved.
There may be provided two each ultrasonic transducers and acoustic
lenses so that a user can clean both hands at the same time.
Preferably, the ultrasonic cleaning machine further comprises an
infrared sensor which serves as a proximity switch, whereby the
ultrasonic cleaning machine is automatically activated when
approach of a human hand is sensed.
In a varied form of the invention, the ultrasonic transmitting and
converging device includes, in place of the aforementioned
ultrasonic transducer and acoustic lens, a plurality of small-sized
ultrasonic vibrating elements arranged on a concave surface of an
array block. This configuration eliminates the need for the
expensive acoustic lens.
According to another aspect of the invention, an ultrasonic
cleaning machine comprises an external tank holding an insulating
oil, an ultrasonic transmitting and converging device immersed in
the insulating oil, a cleaning vessel holding a cleaning liquid,
the cleaning vessel being partially submerged in the insulating
oil, a pair of signal generators for generating signals of two
different frequencies which are used to control output power
radiated by the ultrasonic transmitting and converging device, and
a temperature sensor for sensing temperature of the insulating oil,
wherein ultrasonic waves produced by the ultrasonic transmitting
and converging device converge at a single point within the
cleaning liquid, and wherein the signals of the two different
frequencies for driving an ultrasonic transducer are alternately
chosen based on a duty ratio set in accordance with oil temperature
to provide a constant cleaning effect regardless of oil temperature
variations.
With this arrangement, the ultrasonic transducer is driven at
alternately switch ed two frequencies, of which duty ratio is
determined in accordance with oil temperature. This frequency
switching technique makes it possible to vary the level of cleaning
effect over a remarkably wide range in a stable manner.
According to a further aspect of the invention, an ultrasonic
cleaning machine comprises an external tank holding an cleaning
liquid, and an ultrasonic transducer of which lead wire terminals
are insulated with an insulating material having good thermal
conductivity, the ultrasonic transducer being immersed in the
cleaning liquid, wherein ultrasonic waves produced by the
ultrasonic transducer converge at a single point within the
cleaning liquid.
In this configuration, there is not provided a small-capacity
cleaning vessel and the cleaning liquid filled directly in the
external tank is used as a propagation medium for the ultrasonic
waves as is the case with the conventional type of ultrasonic
cleaning machines. Although lead wire terminals of the ultrasonic
transmitting and converging device must to be insulated with an
insulating material having good heat dissipation efficiency, it is
not necessary to use any insulating oil as an ultrasonic
propagation medium. Naturally, oil temperature compensation is not
required either.
The ultrasonic transmitting and converging device of the this type
of ultrasonic cleaning machine may also include an ultrasonic
transducer and an acoustic lens. The acoustic lens may be mounted
either at a certain height above or in close contact with a
radiating surface of the ultrasonic transducer.
As will be recognized from this summary of the invention, the
ultrasonic cleaning machine employs an ultrasonic transmitting and
converging device, or a combination of an ultrasonic transducer and
acoustic lens. With this arrangement, ultrasonic waves can be
converged at an appropriate position within the cleaning liquid to
increase ultrasonic energy incident upon a unit surface area of an
object to be cleaned. It is therefore possible to obtain a desired
level of cleaning effect without entering excessive power into any
ultrasonic vibrating element. Because the radiating surface of the
transducer or the ultrasonic transmitting and converging device is
not in direct contact with the external tank, audible noise
generation is extremely small. Furthermore, since the transducer,
or the ultrasonic transmitting and converging device, lies within
an insulating oil or a molding resin, or a combination of both,
heat resulting from ultrasonic wave generation is effectively
dissipated so that the risk of overheating is minimized.
Other objects, features and advantages of the invention will be
more fully understood upon reading the detailed description of the
preferred embodiments to follow in conjunction with the
accompanying drawings, in which like reference numerals designate
like elements.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a general configuration diagram of a conventional
ultrasonic cleaning machine;
FIG. 2 is a perspective view schematically illustrating the
internal construction of an ultrasonic cleaning machine according
to a first embodiment of the present invention;
FIG. 3 is a block diagram of a drive/control circuit applicable to
the ultrasonic cleaning machine of FIG. 2;
FIG. 4 is a diagram for explaining the behavior of an acoustic
lens;
FIG. 5 is a graph showing operating characteristics of a
temperature/voltage conversion circuit of FIG. 3;
FIG. 6 is a graph showing operating characteristics of an ON time
control circuit of FIG. 3;
FIG. 7 is a graph showing operating characteristics of an ON time
control circuit of FIG. 3;
FIG. 8 is a block diagram showing an alternative drive/control
circuit applicable to the ultrasonic cleaning machine shown in FIG.
2;
FIG. 9 is a graph showing operating characteristics of an oil
temperature compensating circuit of FIG. 8;
FIG. 10 is a perspective view showing a modified form of the
ultrasonic cleaning machine of FIG. 2 according to a second
embodiment of the invention;
FIG. 11 is a perspective view showing a third embodiment of the
invention;
FIG. 12 is a perspective view showing a fourth embodiment of the
invention;
FIG. 13 is a perspective view showing a fifth embodiment of the
invention;
FIG. 14 is a perspective view showing a modified form of the
ultrasonic cleaning machine of FIG. 13 according to a sixth
embodiment of the invention; and
FIG. 15 is a perspective view showing a seventh embodiment of the
invention .
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
FIG. 2 is a perspective diagram showing the general internal
construction of an ultrasonic cleaning machine according to a first
embodiment of the invention. A pair of ultrasonic transducers 5
(5a, 5b) are fixed to the inside bottom surface of an external tank
51 via vibration-isolating members. Each ultrasonic transducer 5
(5a, 5b) comprises a vibrating element 5-1 and appropriate metallic
matching elements 5-2 and 5-3 that are bonded to the top and bottom
sides of the vibrating element 5-1 to obtain a desired resonance
frequency (28 kHz). A little more than 10 mm above the top surface
of each ultrasonic transducer 5 (5a, 5b), there is provided an
acoustic lens 52 (52a, 52b) for converging ultrasonic waves.
The operation of an acoustic lens is now briefly described.
Although the acoustic lens follows well-known Snell's law as does
an optical lens, it works in a different way on the following
points.
The acoustic lens is usually used in water or other liquid as most
of ultrasonic energy incident upon a lens surface is reflected when
the acoustic lens is used in the atmosphere. A convex optical lens
can still converge a light beam even when it is immersed in water.
This is because light waves propagate at a lower velocity in lens
body than in water, as is the case when the lens is used in the
air. Contrarily, the propagating velocity of sound waves is higher
in lens body than in water or air and, therefore, a sound beam is
converged by an acoustic concave lens, unlike the case with the
optical lens. The aforementioned behavior of the acoustic lens is
now described in further detail using Snell's law. Referring to
FIG. 4, there is shown an acoustic lens made of an acrylic plate.
Here, it is assumed that the sound velocity C.sub.1 within the
acoustic lens is 2500 m/sec., and the sound velocity C.sub.2 in
water is 1400 m/sec. If .theta..sub.1 is the angle of incidence,
and .theta..sub.2 the angle of refraction, measured from the
interface between the lens and water when sound waves pass from the
lens to water, C.sub.1 /C.sub.2 =cos.theta..sub.1
/cos.theta..sub.2. It is apparent from this equation that
.theta..sub.1 <.theta..sub.2 because C.sub.1 >C.sub.2. It
follows that sound waves passing through the acoustic concave lens
at right angles thereto converge as shown in FIG. 4.
Referring again to FIG. 2, there is provided a small-capacity
cleaning vessel 53 having a one-piece formed pair of washbowls
above the acoustic lenses 52, covering the top of the external tank
51. The cleaning vessel 53 holds a cleaning liquid X which may be
water or a solution of detergent while the external tank 51 is
filled with insulating oil Y (e.g., mineral oil or synthetic oil)
almost to the top surface of the cleaning vessel 53 and
hermetically sealed. The ultrasonic transducers 5 and acoustic
lenses 52 are therefore completely immersed in the oil Y. A narrow
air gap is left above the surface of the oil Y, within the external
tank 51. This is to protect the external tank 51 from expansion of
the oil Y due to its temperature variations. Shown by the numeral 6
is a thermistor for sensing oil temperature.
The focal length of each acoustic lens 52 (52a, 52b) is 60 mm in
water. If the bottom of the cleaning vessel 53 is positioned 30 mm
above the acoustic lenses 52, converging points (or focal points)
of ultrasonic waves are located 30 mm above the bottom of the
cleaning vessel 53 (since the sound velocity in the cleaning liquid
X is almost same as in the oil Y). If the ultrasonic cleaning
machine is used as a fingernail cleaner as shown in FIG. 2, the
focal points occur approximately at distal interphalangeal joints
of human hands when they are soaked in the cleaning vessel 53.
FIG. 3 is a block diagram showing a drive/control circuit for
controlling and driving the ultrasonic cleaning machine of FIG.
2.
Designated by the numeral 61 (61a, 61b) are oscillating circuits
for generating a 20 kHz signal (non-resonant frequency); and
designated by the numeral 62 (62a, 62b) are oscillating circuits
for generating a 28 kHz signal (resonant frequency). Designated by
the numeral 63 (63a, 63b) are switching circuits for alternately
switching between the 20 kHz and 28 kHz signals fed from the
respective oscillating circuits 61, 62. More specifically, each
switching circuit 63 (63a, 63b) selects the 28 kHz oscillating
circuit 62 (62a, 62b) when an ON signal is transmitted from a
later-described ON time control circuit 66, the 20 kHz oscillating
circuit 61 (61a, 61b) when an OFF signal is transmitted from the ON
time control circuit 66. Designated by the numeral 64 (64a, 64b)
are power amplifiers for driving the respective ultrasonic
transducers 5 (5a, 5b). Each power amplifier 64 (64a, 64b)
amplifies the output signal of the 20 kHz oscillating circuit 61
(61a, 61b) or 28 kHz oscillating circuit 62 (62a, 62b) whichever
selected by the switching circuit 63 (63a, 63b) when an ON signal
is received from a later-described ON/OFF control circuit 69. It is
to be noted that the circuits (61a, 62a, 63a and 64a) for driving
the ultrasonic transducer 5a are identical to the circuits (61b,
62b, 63b and 64b) for driving the ultrasonic transducer 5b. If the
ultrasonic cleaning machine is of a single transducer type as in a
later-described second embodiment, there should be provided only
one set of these circuits.
When an ultrasonic transducer is immersed in oil as is the case
with the present embodiment, variations in oil viscosity due to oil
temperature changes significantly affect ultrasonic propagating
conditions. This has great impact on the cleaning effect. To
maintain a constant level of cleaning effect, the ultrasonic
cleaning machine of this embodiment is provided with a circuit for
oil temperature compensation, which will be described in detail
below.
Referring to FIG. 3, the numeral 6 shows the earlier-mentioned
thermistor. Designated by the numeral 65 is a temperature/voltage
conversion circuit which converts a temperature signal fed from the
thermistor 6 to a voltage signal. Operating characteristics of the
temperature/voltage conversion circuit 65 are shown in FIG. 5. The
ON time control circuit 66 sets a duty ratio, or the ratio of an ON
signal period to a predetermined cycle time (150 msec. in this
embodiment), in accordance with the output voltage of the
temperature/voltage conversion circuit 65. As shown in FIG. 6, when
the output voltage of the temperature/voltage conversion circuit 65
is 5 V (oil temperature 30.degree. C.) or less, the duty ratio is
set to 100%, whereby the ON time control circuit 66 continuously
outputs an ON signal. When the output voltage is above 5 V but no
more than 7.5 V (oil temperature 30.degree. C. to 50.degree. C.),
the duty ratio is set to 75%, whereby ON signal and OFF signal
periods become 112.5 msec. and 37.5 msec., respectively, as shown
in FIG. 7. When the output voltage is above 7.5 V but no more than
10 V (oil temperature 50.degree. C., to 70.degree. C.), the duty
ratio is set to 50%, whereby both ON signal and OFF signal periods
become 75 msec. When the output voltage becomes 10 V (oil
temperature 70.degree. C.) or above, the duty ratio is set to 0%,
whereby the ON time control circuit 66 continuously outputs an OFF
signal. When transmitting a continuous OFF signal for 0% duty ratio
to the switching circuits 63 (63a, 63b), the ON time control
circuit 66 outputs a stop signal to the ON/OFF control circuit 69
at the same time.
Designated by the numeral 67 is a push-button switch which is
pressed each time the ultrasonic cleaning machine is used.
Designated by the numeral 68 is a timer on which a desired cleaning
time can be set. The timer 68 transmits a start signal to the
ON/OFF control circuit 69 when an ON signal is entered from the
push-button switch 67, a stop signal when the set cleaning time
elapses. The ON/OFF control circuit 69 transmits ON or OFF signals
to the power amplifiers 64 (64a, 64b) in response to the start and
stop signals received from the timer 68. The ON/OFF control circuit
69 turns off the power amplifiers 64 (64a, 64b) when the stop
signal is entered not only from the timer 68 but also from the ON
time control circuit 66 (when the oil temperature becomes
70.degree. C. or above).
When a user turns on an unillustrated main switch, individual
circuits including the oscillating circuits 61, 62 are energized
and the ultrasonic cleaning machine becomes ready to operate. At
this point, the thermistor 6 senses oil temperature. If the oil
temperature is 35.degree. C., for instance, the duty ratio is set
to 75% so that the ON time control circuit 66 outputs an ON signal
for a period of 112.5 msec. within each successive 150 msec. cycle
time. During each ON signal period, the 28 kHz signal is supplied
to the power amplifiers 64 (64a, 64b). Similarly, the ON time
control circuit 66 outputs an OFF signal for a period of 37.5 msec.
within each successive cycle time. The 20 kHz signal is supplied to
the power amplifiers 64 (64a, 64b) during each OFF signal period.
The 28 kHz and 20 kHz signals are therefore alternately fed into
the power amplifiers 64 (64a, 64b) at a regularly recurrent duty
cycle, as shown in FIG. 7.
When the push-button switch 67 is pressed, the timer 68 begins to
count up and transmits a start signal to the ON/OFF control circuit
69. As a result, the ON/OFF control circuit 69 causes both of the
power amplifiers 64 (64a, 64b) to turn on, whereby each ultrasonic
transducer 5 (5a, 5b) is alternately driven by the 28 kHz and 20
kHz signals in accordance with the aforementioned duty ratio. When
using the ultrasonic cleaning machine for removing dirt from
fingernails, the user should soak his or her hands into the
cleaning liquid X in the cleaning vessel 53 in such a manner that
the fingernails are located at converging points of ultrasonic
waves.
When the timer 68 reaches the set cleaning time, the ON/OFF control
circuit 69 outputs a stop signal. Since the power amplifiers 64
(64a, 64b) are turned off at this point, the ultrasonic cleaning
machine stops cleaning operation.
On the other hand, if the oil temperature reaches 50.degree. C. due
to heat buildup in the ultrasonic transducers 5 (5a, 5b) after
prolonged cleaning operation, for instance, ultrasonic energy
incident upon a unit surface area of an object to be cleaned
exceeds a permissible level. In this case, ultrasonic energy
emitted from the ultrasonic transducers 5 (5a, 5b) is suppressed to
maintain a constant level of cleaning effect. More particularly,
the duty ratio is set to 50% so that the ultrasonic transducers 5
(5a, 5b) are driven for shorter time periods at 28 kHz, and longer
time periods at 20 kHz, compared to the duty ratio of 75%.
Should the oil temperature exceeds 70.degree. C. during cleaning
operation, the ON time control circuit 66 transmits a stop signal
to the ON/OFF control circuit 69 and the cleaning operation is
interrupted.
When the duty ratio is lowered, or when the time periods of 28 kHz
transmission are reduced, the total output power from the
ultrasonic transducers 5 (5a, 5b) decreases. The reason for the
decrease in the output power is as follows. The ultrasonic
transducers 5 (5a, 5b) resonate when driven at 28 kHz. They are not
in a resonant condition when driven at 20 kHz. The ultrasonic
transducers 5 (5a, 5b) have small impedance at the resonant
frequency. Their impedance increases when the excitation frequency
deviates from the resonant frequency. Since the power amplifiers 64
(64a, 64b) that drive the ultrasonic transducers 5 (5a, 5b) have a
constant voltage characteristic, the input power to each ultrasonic
transducer 5 (5a, 5b) decreases to about one fifth (1/5) when the
excitation frequency is altered from 28 kHz to 20 kHz. The output
power, or emitted ultrasonic energy, decreases accordingly.
Provided that the input power to each ultrasonic transducer 5 (5a,
5b) is 100 W at 100% duty ratio, the input power at 0% duty ratio
becomes 20 W, or one fifth of 100 W.
Generally, mean input power P [W] at a duty ratio of D% is given by
the following equation: ##EQU1##
Thus, mean input power is 80 W when the duty ratio is 75%, 60 W
when the duty ratio is 50%. If energy conversion efficiency of each
ultrasonic transducer 5 (5a, 5b) is .eta., its output power is
reduced from 100 .eta.W to 80 .eta.W and 60 .eta.W at 75% and 50%
duty ratios, respectively. During OFF periods when each ultrasonic
transducer 5 (5a, 5b) is driven at 20 kHz, its output power becomes
20 .eta.W. When the ultrasonic output power is reduced to such a
low level, the cleaning effect decreases almost zero. As seen
above, the cleaning effect decreases from 100% to 75% and 50% when
the duty ratio is reduced from 100% to 75% and 50%,
respectively.
It would be possible to alternately energize and de-energize the
ultrasonic transducers 5 (5a, 5b) at a fixed frequency of 28 kHz at
intervals equivalent to the earlier-mentioned ON and OFF cycle
times rather than switching the excitation frequency between 28 and
20 kHz. In this case, mean input power to the ultrasonic
transducers 5 (5a, 5b) can be arbitrarily varied by altering each
successive energized or ON period. However, this form of
intermittent activation is not preferable because parasitic
oscillation occurs every time the ultrasonic transducers 5 (5a, 5b)
are turned on and off.
It would be appreciated from the above discussion that the cleaning
effect can be widely varied in a stable manner with the
drive/control circuit of FIG. 3. On the other hand, if the
viscosity of the oil Y is not affected to a great extent by its
temperature, or if a satisfactory level of cleaning effect can be
maintained with an adjustable range of 0 to 20%, a drive/control
circuit having a simplified oil temperature compensating circuit
for controlling power amplifiers like the example shown in FIG. 8
will be sufficient.
Referring to FIG. 8, designated by the numeral 1 is a power supply
circuit for providing a line voltage to individual circuits of the
ultrasonic cleaning machine as well as driving power to power
controllers 2 (2a, 2b). Designated by the numeral 3 (3a, 3b) are
oscillating circuits for generating an ultrasonic frequency of 28
kHz and designated by the numeral 4 (4a, 4b) are power amplifiers
for amplifying the 28 kHz signal fed from the oscillating circuits
3 (3a, 3b) to provide increased output power. The power controllers
2 (2a, 2b) control collector voltage of final-stage transistors of
the individual power amplifiers 4 (4a, 4b). Shown by the numeral 5
(5a, 5b) are ultrasonic transducers.
Designated by the numeral 6 is a thermistor and designated by the
numeral 7 is an oil temperature compensating circuit. The oil
temperature compensating circuit 7 controls the power controllers 2
(2a, 2b) to compensate for oil temperature variations based on
temperature sensed by the thermistor 6 so that the collector
voltage (and, accordingly, the output power) of the individual
power amplifiers 4 (4a, 4b) is varied in accordance with
characteristic lines graphed in FIG. 9.
In FIG. 8, designated by the numeral 8 is an infrared sensor for
detecting a human hand when it is placed in the cleaning vessel 53.
A pyroelectric-cell-type sensing device is used to prevent
accidental detection of human body in the proximity. The infrared
sensor 8 is mounted on the periphery of the cleaning vessel 53
shown in FIG. 2, for instance. Designated by the numeral 9 is a
timer on which a desired cleaning time can be set. The timer 9
transmits an ON signal when a detection signal is entered from the
infrared sensor 8, an OFF signal when the set cleaning time
elapses. Indicated by the numeral 10 is an ON/OFF control circuit
which activates and deactivates the power amplifiers 4 (4a, 4b) in
accordance with the ON and OFF signals fed from the timer 9. The
ON/OFF control circuit 10 automatically turns off the power
amplifiers 4 (4a, 4b) when the oil temperature reaches 65.degree.
C. and a specific signal is transmitted from the oil temperature
compensating circuit 7, as shown in FIG. 9.
According to the drive/control circuit of FIG. 8, if the oil
temperature within the external tank 51 is 30.degree. C. or less,
the power amplifiers 4 (4a, 4b) are driven at 130% of their normal
input power, and when the oil temperature rises beyond 30.degree.
C., the output power of the power amplifiers 4 (4a, 4b) is reduced,
as shown in FIG. 5. With this arrangement, ultrasonic energy
incident upon a unit surface area of human hands soaked in the
cleaning liquid X is regulated to a constant level.
Since the drive/control circuit of FIG. 8 is provided with the
infrared sensor 8 which works as a proximity switch, there is no
need to operate any ON/OFF switch with a wet hand. This is
convenient when the ultrasonic cleaning machine has a
double-washbowl cleaning vessel as in the example of FIG. 2.
Although the embodiment of FIG. 2 employs a double-washbowl
configuration comprising a pair of ultrasonic transducers 5 (5a,
5b) and to allow simultaneous cleaning of both hands, it may be
modified to a single-washball configuration (second embodiment) as
shown in FIG. 10 if it is not required to clean both hands at the
same time.
In FIGS. 2 and 10, each acoustic lens 52 is provided at a certain
distance from the radiating surface (or the upper end face) of the
associated ultrasonic transducer 5. Naturally, there is the need
for a support mechanism for retaining each acoustic lens 52 in
position. From this, it would be recognized that if this lens
retaining mechanism is constructed to enable up/down movements of
the acoustic lens 52, it is possible to move the converging point
of ultrasonic waves, or the point of maximum cleaning effect, to a
desired position depending on the shape of the cleaning vessel 53
or the type of objects to be cleaned.
FIG. 11 is a diagram showing one variation of the ultrasonic
cleaning machine of FIG. 10 according to a third embodiment of the
invention, in which the acoustic lens 52 is mounted in direct
contact with the radiating surface of the ultrasonic transducer 5.
In the embodiment of FIG. 11, the point of maximum cleaning effect
(or the converging point of ultrasonic waves) within a cleaning
liquid in the cleaning vessel 53 is set to 60 mm. This
configuration is advantageous in that the machine structure can be
simplified because the lens retaining mechanism is not required at
all. Although the acoustic lens 52 may vibrate producing quite a
small sound within the audible frequency range, the sound will
never leak to the outside passing through the oil Y and external
tank 51.
FIG. 12 is a perspective view showing a fourth embodiment of the
invention. This embodiment employs, instead of the vibrating
elements 5-1 and acoustic lenses 52 of the foregoing embodiments,
an ultrasonic transmitting and converging device 50 for
simultaneously emitting and converging ultrasonic waves. The
ultrasonic transmitting and converging device 50 comprises an array
block 50-1 having a concave upper surface and a plurality of
circular vibrating elements 50-2 arranged on the upper surface of
the array block 50-1. According to this configuration, the
expensive acoustic lens 52 is not required at all and the overall
construction of the ultrasonic cleaning machine is simplified.
Advantages of providing the independent cleaning vessel 53 for
holding the cleaning liquid X besides the external tank 51 as shown
in FIGS. 2, 10, 11 and 12 are as follows:
(1) It is possible to reduce the amount of the cleaning liquid X to
be replaced at one time when it has been contaminated after
repeated use. It should be noted that the oil Y within the external
tank 51 need not be replaced.
(2) A liquid having high transmitting efficiency can be employed as
a medium for propagating ultrasonic vibrations produced by the
ultrasonic transducers 5 or ultrasonic transmitting and converging
device 50.
(3) It is possible to eliminate the need to insulate the terminals
5-4, lead wires 5-5 and outlet terminals 5-6 of the ultrasonic
transducers 5 by using insulating oil as a transmitting medium.
(4) The cleaning vessel 53 may be made of a plastic material,
instead of a metallic material, and can be formed into an optimum
shape depending on the shape of objects to be cleaned.
The invention is also applicable to such ultrasonic cleaning
machines that hold a cleaning liquid X directly in an external tank
51 as is the case with the conventional ultrasonic cleaning
machines.
FIG. 13 shows this type of ultrasonic cleaning machine as a fifth
embodiment of the invention. According to the configuration of FIG.
13, the cleaning liquid X, which is generally electrically
conductive, is filled directly in the external tank 51. It is
therefore necessary to insulate electric connections around the
individual transducers 5. For this reason, transducer terminals
5-4, lead wires 5-5 and outlet terminals 5-6 are insulated by
filling an insulating material Z around the lower section of each
transducer 5. Since the insulating material Z is required to have
good thermal conductivity for accelerating heat dissipation from
the transducers 5, a molding resin is used in this embodiment.
FIG. 14 shows a sixth embodiment of the invention, which is a
modification of the fifth embodiment. This is a single-washball
version (comprising one each transducer 5 and acoustic lens 52) of
the ultrasonic cleaning machine of FIG. 13.
FIG. 15 shows a seventh embodiment of the invention, which is a
modification of the sixth embodiment of FIG. 14. In this
embodiment, the acoustic lens 52 is in direct contact with the
ultrasonic transducer 5.
Advantages of holding the cleaning liquid X directly in the
external tank 51 as seen in FIGS. 13, 14 and 15 are as follows:
(1) Since a low-viscosity cleaning liquid is used as a medium for
ultrasonic waves, ultrasonic propagation characteristics are almost
unaffected by changes in the liquid temperature. Therefore, the
drive/control circuit of FIG. 8 is suited for this configuration
except that the thermistor 6 and oil temperature compensating
circuit 7 are not necessary. Furthermore, it is also possible to
eliminate the power controllers 2, resulting in simplification of
the drive/control circuit.
(2) Mechanical construction of the ultrasonic cleaning machine can
be much simplified. (In the configuration using oil as a
propagation medium, an arrangement for sealing an oil-containing
tank is inevitably required.)
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